Photovoltaic (PV) arrays are formed by mechanically linking together PV modules into an array. Most PV module coupling systems require the time-consuming use of multiple small fasteners. High part count and slow installation time is a major barrier to reducing PV system costs and adoption. Some attempts have been made to reduce fastener usage by developing press-fit and hook-type connections. However, these systems suffer from a number of drawbacks.
First, neither of these methods can adequately account for variations in the dimensions of PV modules and couplings due to manufacturing tolerances. PV modules typically vary by approximately ±0.10″ along the length and/or width dimension. When multiple modules are formed into columns in the north-south direction of the PV array, it is critical that any dimensional variations from one module in the column not carry forward to the next module in the column, as the dimensional variations will add up over the length of the column and result in significant dimensional differences from one column to the next. Likewise, the same problem exists with east-west rows of PV modules. This problem, frequently referred to as tolerance take-up, is solved in rail-based systems by spacing the modules in a column more or less from each other on top of mounting rails so that the next module in the column is properly positioned and/or by only linking modules to the rails along one axis, either east-west or north-south. However, in rail-free systems, a PV module is structurally connected to the next module in both the north-south direction and the east-west direction. Thus, if the seams between adjacent east-west modules do not line up because of compounded north-south dimensional variations, then it may be impossible to complete the installation of an array. In other systems compounded east-west variations may cause problems along the north-south axis. Press-fit and hook-type connections do not adequately address or solve the problem of tolerance variations.
Second, press-fit and hook-type connections do not provide a reliable electrical ground bond between adjacent PV modules. Hook-type connections are inherently loose-fitting and thus incapable of providing a consistent, low-resistance ground bond that will withstand weather conditions over time. Similarly, a press-fit connection does not provide a reliable ground bond unless the materials are deformed enough in the connection. In practice, too much force is required to achieve such deformation with standard PV module frame materials such as aluminum, thereby eliminating any time and cost savings that might have occurred since a heavy-duty tool would be required to deliver the force needed for the deformation.
Third, press-fit and hook-type systems cannot reliably provide a strong, durable connection between mating male and female parts. In order to facilitate a quick and easy connection, the female receiving portion in the connection is made wider than the male connecting portion. This results in a loose or unstable connection, which is vulnerable to loosening over time as the PV modules experience mechanical stress due to wind and snow loads.
It is also important to note that PV mounting systems require a design that works with a wide tolerance band. The reason is that production of tight tolerance PV modules and couplings is very expensive. In order to accelerate the adoption of solar power, it is necessary to reduce the cost of solar arrays, thus increased costs for tight tolerance parts is not a viable option in the market.